In historiography and genocide studies, cumulative radicalization is the notion that genocide and other mass crimes are not planned long in advance, but emerge from wartime crises and a process of radicalization. Originally coined by German historian Hans Mommsen with regard to the functionalist view of the Holocaust, in his 1976 essay "National Socialism: Cumulative Radicalization and the Regime's Self-Destruction". The concept has also been applied to the Armenian genocide.
Mommsen's concept of 'cumulative radicalization' was first proposed, I believe, in his 1976 entry for 'National Socialism' in the ninth edition of Meyers Enzyklopädisches Lexikon—the final edition of this venerable publication. His six-page essay, under the title 'Der Nationalsozialismus. Kumulative Radikalisierung und Selbstzerstörung des Regimes' ('National Socialism: Cumulative Radicalization and the Regime's Self-Destruction'), is a condensation of ideas that he had been developing since he had begun to work on the history of Nazism in the early 1960s; to appropriate John Stuart Mill's phrase, it appears as a kind of 'intellectual pemmican', almost too dense to digest... Mommsen's Third Reich is an object lesson in how conservative elites chose compromise with regimes of totalitarian terror, why they failed to resist and how difficult it therefore was for domestic forces to dislodge this kind of terroristic regime— unless it could be toppled by its own excessive ambitions, in the parasitic dynamic indicated by the essay's title.